A high affinity (Ka equals 4 X 10 to the minus 9th power M), stereospecific binding site for d-LSD has been recently identified in homogenates of the rat brain. Serotonin was shown to be the only putative neurotransmitter that could effectively displace d-LSD from this binding site. Since d-LSD has a powerful inhibitory effect on the serotonin containing neurons of the midbrain it was proposed that the identified binding site was a serotonin receptor. Since the examination of the properties of other spectific binding sites have produced valuable information about the pharmacology and/or physiology of the particular ligand which binds to these sites or receptors, there is every reason to expect that an investigation into the properties of specific d-LSD binding might be helpful in advancing our understanding about the pharmacology of this drug. Previous research on d-LSD binding clearly indicates the need for an examination of the physical and chemical properties of this in vitro binding process. Thus, the proposed research plan will attempt to determine the effects of various inorganic ions, chelating agents, enzymes, protein modifying reagents, d-LSD and serotonin analogs, etc. on specific d-LSD binding in crude and purified fractions of brain homogenates. It is hoped that the results from the proposed research will provide additional insights as to why this drug is such a powerful hallucinogen.